Copy Number Variation and SNP Affect Egg Production in Chickens by Regulating AP2M1 Expression to Inhibit GnRH...

Deciphering egg laying-related genetic basis and aggregating its key genes or genetic markers will be helpful for genetic improvement of chicken laying-oriented breeding. Our previous research found adaptor related protein complex 2 mu 1 subunit (AP2M1) gene is a key candidate gene related to egg production. However, its functions and genetic regulatory mechanisms remain unclear. This study aims to clarify AP2M1 functions and identify its functional variants. Expression characteristic analysis of AP2M1 within and between breeds confirmed the negative regulatory relationship of hypothalamic AP2M1 expression on egg production. Overexpression and interference tests indicated that AP2M1 inhibited GnRH synthesis and secretion in chicken hypothalamic neuron cells. To explore molecular markers influencing AP2M1 expression, a copy number variation (CNV) region containing AP2M1 were verified in different chicken breeds by qRT-PCR; a copy number loss of AP2M1 were observed in layers compared to native breeds, commercial broilers, and wild breed. Correlation analysis between CNV and egg number, as well as differential expression analysis of different copy numbers, indicated that the CNV contributed to the differences in egg production by influencing AP2M1 expression. Meanwhile, through association analysis of whole-genome SNPs in AP2M1 with 13 egg production traits, 15 egg-laying related SNPs were identified. Further difference expression analysis among the different genotypes of SNPs and dual-luciferase reporter assay confirmed that chr9:15994879T>C was a functional SNP regulating AP2M1 expression. These findings unveil egg laying-related functional molecular markers will help accelerate molecular design breeding process of chicken egg production.